Inverts the colors of all line and text objects from the imported file to Revit-specific colors. Dark colors become lighter, and light colors become darker. This can improve readability when the file is in Revit. This option is set by default.
The following image is a small sample of what occurs. The top row of lines, imported using Preserve, have been assigned to the basic color palette and a couple extended colors, such as Red, Yellow, Blue and #10 (red) and #30 (amber). The bottom row of lines, imported using Invert, are how they are changed from the colors assigned in the CAD file once they are represented in Revit.
Looking closely, red becomes cyan. If you examine #10, a red also, you'll see that the Inverted color is also cyan or at least cyanish. Shades of red will be converted to shades of cyan. Compare the others and you'll see similar logic.
I don't use Invert, or recommend doing so, because the results are rarely meaningful or useful. You don't know why something is assigned to a given color. The simplistic goal is to just reverse (invert) the intensity of the color once it is imported, to make it easier to see on a white background or balance their appearance in this way.
If we really want to retain or use the color in some way then I believe it is better to keep (preserve) the colors we may already be familiar with, at least if we are responsible for creating that data too. That's my two pence worth.